The XtMalloc functions returns
a pointer to a block of storage of at least the specified size bytes. If
there is insufficient memory to allocate the new block, XtMalloc calls
XtErrorMsg.

The XtCalloc function allocates space for the specified
number of array elements of the specified size and initializes the space
to zero. If there is insufficient memory to allocate the new block, XtCalloc
calls XtErrorMsg.

The XtRealloc function changes the size of a block
of storage (possibly moving it). Then, it copies the old contents (or as
much as will fit) into the new block and frees the old block. If there is
insufficient memory to allocate the new block, XtRealloc calls XtErrorMsg.
If ptr is NULL, XtRealloc allocates the new storage without copying
the old contents; that is, it simply calls XtMalloc.

The XtFree function
returns storage and allows it to be reused. If ptr is NULL, XtFree returns
immediately.

XtNew returns a pointer to the allocated storage. If there
is insufficient memory to allocate the new block, XtNew calls XtErrorMsg.
XtNew is a convenience macro that calls XtMalloc with the following
arguments specified:

0>=40 .vs 0u
0<=39 .vs 0p
((type *) XtMalloc((unsigned) sizeof(type))

XtNewString returns a pointer to the allocated storage. If there is insufficient
memory to allocate the new block, XtNewString calls XtErrorMsg. XtNewString
is a convenience macro that calls XtMalloc with the following arguments
specified: